Oxygen/glucose deprived cortical cell cultures were used to explore the involvement of calcium in the mechanism of hypoxic/hypoglycemic insults and protection of nerve growth factor (NGF). Neuron viability and lactate dehydrogenase(LDH) efflux in the bathing medium of cerebral cortex cultures of fetal rats were measured as indication of the NGF effect. Calcium fluorescence indicator Fura-2/AM was used to measure free intracellular calcium([Ca2+]i). When cultures were deprived of oxygen/glucose, massive neuronal death occurred 16-24 h following the onset of hypoxia/hypoglycemia. NGF(3-100 micrograms.L-1) dose-dependenly attenuated the 24 h hypoxia/hypoglycemia-induced efflux of LDH and elevated the number of surviving neurons. Hypoxia/hypoglycemia induced a reduction in [Ca2+]i in early stage and then a large elevation of [Ca2+]i in 12-24 h. NGF 50 micrograms.L-1 brought [Ca2+]i to normal limits during the early stage of hypoxia/hypoglycemia and prevented the later elevation in [Ca2+]i. The [Ca2+]i elevation may be involved in the cell damage in hypoxia/hypoglycemia deprived cultures. It is believed that NGF protect cerebral cortical neurons against hypoxic/hypoglycemic insults via 'stabilizing' [Ca2+]i level or preventing the late rise in [Ca2+]i.